Think small variations in temperature and precipitation levels don't have much of an impact? Guess again. A prolonged period of wet weather spurred the spread of the Bubonic plague in medieval times, according to a new study. And a 300-year spell of unpredictable weather coincided with the decline of the Roman Empire.

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Climate change wasn't necessarily the cause of these and other major historical events, researchers say. But the study, which pieced together a year-by-year history of temperature and precipitation in Western Europe, dating back 2,500 years, offers the most detailed picture yet of how climate and society have been intertwined for millennia.

"We need to have a better understanding about the ancient climate system and its variability to understand the modern situation," said Ulf Büntgen, a paleoclimatologist at the Swiss Federal Research Institute in Zurich. "It does not provide any predictions. But it helps us take it as something to be considered."

Büntgen and colleagues collaborated with archaeologists to amass a database of more than 9,000 pieces of wood dating back 2,500 years. Samples came from both live trees and remains of buildings and other wooden artifacts, all from France and Germany. By measuring the width of annual growth rings in the wood, the researchers were able to determine temperature and precipitation levels on a year-by-year basis.